Master cylinder

ABSTRACT

A master cylinder for the clutch or brake of a motor vehicle has a housing for a reciprocable piston one end of which receives the spherical head of a reciprocable piston rod. The head is held in a desired position relative to the piston by a one-piece or composite coupling device having a first section exerting a pull or bearing upon the head of the piston rod and a second section which is confined in or surrounds the end of the piston and urges the first section in a direction to hold the piston rod against axial movements relative to the piston. The coupling device and/or the piston are or can be made of a plastic material, and the connection between such parts is or can be established by snap action.

This application is a continuation of PCT/EP98/06782 filed on Oct. 26,1998.

BACKGROUND OF THE INVENTION

The invention relates to improvements in fluid-operatedcylinder-and-piston assemblies in general, and more particularly toassemblies known as master cylinders. A master cylinder can be utilized,for example, in a motor vehicle where it can form part of a device suchas a hydraulic brake or clutch.

As a rule, a master cylinder comprises a cylinder or housing defining achamber for a reciprocable piston which can displace a column of liquidto thus actuate a brake or a clutch, e.g., by way of a so-called slavecylinder. “Modern Automotive Technology” (authored by James E. Duffy andpublished by The Goodheart-Willcox Company, Inc. of Tinley Park, Ill.)defines a master cylinder for a brake pedal assembly as a foot-operatedpump that forces liquid into the brake lines and wheel cylinders. Itsbasic functions are to develop pressure, causing the wheel cylinderpistons to move toward rotors or drums; to help equalize the pressurerequired for braking after all of the shoes or pads produce sufficientfriction; to keep the system full of fluid as the brake linings wear;and to maintain slight pressure to keep contaminants (such as air and/orwater) from entering the system.

A master cylinder can be assembled with a brake pedal or with a clutchpedal to form part of a module which is ready to be installed in a motorvehicle, e.g., to apply brakes to the wheels or to engage or disengage afriction clutch. In many master cylinders, the brake pedal or clutchpedal is linked to a piston rod having a free end provided with aspherical head which is connected to and can swivel relative to thepiston in the housing of the master cylinder. The module can beinstalled on a wall, e.g., between the space for the prime mover and thedriver compartment. The piston can displace a column of liquid in orderto cause the piston of a slave cylinder to expel liquid from the housingof the slave cylinder or to permit liquid to reenter the housing.

Reference may be had, for example, to published German patentapplication Ser. No. 196 08 132 A1 which describes and shows aconventional master cylinder. The latter comprises a housing made of aplastic material and defining a chamber for a plastic piston. The pistonrod of the master cylinder has a spherical head which is form-lockinglyconnected with the piston. To this end, the piston is provided with asocket having a recess bounded by a concave surace and serving toreceive the head of the piston rod (reference may be had to FIG. 3 ofthe German published application). The piston is slotted axially in theregion of the head of the piston rod so that the head can be readilyintroduced into the socket. A firm swiveling connection between the headof the piston rod and the piston is established by a sleeve which isslipped onto the slotted part of the piston so that the latter snuglysurrounds the head and prevents separation of the spherical head fromthe piston.

A drawback of such master cylinders is that at least the slotted end ofthe piston and/or the head of the piston rod (also called push rod) mustbe made of a highly elastic material in order to permit the head of thepiston rod to enter the cavity of the socket in the piston. As a rule,the head of the piston rod and/or the piston must be made of anelastomeric material, particularly a thermoplastic material whichpermits adequate deformation of the head and/or of the adjacent end ofthe piston and to thus permit insertion of the head into its socket. Inmany instances, the thermal expansion coefficient of a thermoplasticmaterial is very high and actually too high because the stability of thepiston is not sufficient for the intended purpose. In other words, thestability of the entire master cylinder is unsatisfactory for theintended purpose e.g., for use in a brake system or in combination witha clutch in the power train of a motor vehicle.

The manner in which an electronically controlled or operated mastercylinder can regulate the operation of a clutch by way of a slavecylinder in the power train of a motor vehicle is described and shown,for example, in commonly owned U.S. Pat. No. 5,725,456 granted Mar. 10,1998 to Robert FISCHER et al. for “METHOD OF REGULATING THE OPERATION OFA TORQUE TRANSMISSION APPARATUS”. The disclosure of the commonly ownedpriority application Ser. No. 197 52 076.6, as well as the disclosure ofeach U.S. and foreign patent and patent application identified in thespecification of the present application are incorporated herein byreference.

OBJECTS OF THE INVENTION

An object of the present invention is to provide a master cylinderwherein the connection between the piston and the piston rod is morereliable than in heretofore known master cylinders.

Another object of the invention is to provide a relatively simple andinexpensive but higly reliable swivel joint between the piston and thespherical head of the piston rod or push rod in a master cylinder whichis suitable for use in the power train between the prime mover (such asan internal combustion engine) and the wheels of a motor vehicle.

A further object of the invention is to provide a novel and improvedarrangement which couples a female part to a spherical male part in sucha way that the force with which a separation of the male part from thefemale part is opposed invariably exceeds a preselected lower thresholdvalue irrespective of the orientation of male and female parts relativeto each other.

An additional object of the invention is to provide a novel piston foruse in the above outlined master cylinder.

Still another object of the invention is to provide a novel and improvedreliable (but separable, if and when necessary) joint between the pistonand the piston rod in the chamber of a housing forming part of a mastercylinder for use in conjunction with the braking system or with a clutchin the power train of a motor vehicle.

A further object of the invention is to provide a master cylinderadapted to be utilized as a superior (e.g., longer-lasting) substitutefor conventional master cylinders which are presently employed in thepower trains of motor vehicles.

An additional object of the invention is to provide a master cylinderwhich constitutes a less expensive, more reliable, more compact and morereadily assemblable and/or disassemblable substitute for presently knownmaster cylinders.

Another object of the invention is to provide a novel and improvedmethod of connecting the spherical head of a piston rod or push rod withthe piston of a master cylinder.

Still another object of the invention is to provide a module wherein thepiston and the spherical head of a piston rod are assembled with eachother in a novel and improved way with freedom of swivelling movementrelative to each other and in a condition of readiness for installationin the housing of a master cylinder for use in conjunction with thebraking system or with a friction clutch in the power train of a motorvehicle.

A further object of the invention is to provide a module which formspart of a master cylinder and can be installed in the housing of amaster cylinder in a simple and reliable manner, be it in conjunctionwith one or more brakes or in conjunction with a friction clutch.

An additional object of the invention is to provide a highly compact andlightweight master cylinder for use in the power train of a motorvehicle.

SUMMARY OF THE INVENTION

The invention is embodied in a cylinder and piston assembly,particularly in a master cylinder, which comprises a housing defining achamber, a piston which is reciprocable in the chamber, a reciprocablepiston rod including a spherical head extending into the chamber intoengagement with one end of the piston, and means for articulatelycoupling the head to the one end of the piston. The coupling meansincludes a first section which engages the piston rod and a secondsection which is affixed to the piston.

The piston is or can be made of a plastic material, and at least aportion of the coupling means can consist of a metallic sheet material,i.e., such portion of the coupling means can constitute a suitablydeformed sheet metal blank.

In accordance with a first embodiment of the invention, the firstsection of the coupling means can constitute a portion of a hollowsphere which surrounds and bears upon a portion of the head and has acentral opening remote from the second section of such coupling meansand surrounding a portion of piston rod. The piston rod further includesan elongated part having an end connected to (e.g., of one piece with)the spherical head; the first section of the coupling means surroundsthe head at the end of the elongated part of the piston rod, and thesecond section can include a tubular portion surrounding the one end ofthe piston. The one end of the piston can be provided with acircumferentially complete or multiple-section external groove, and thesecond section of the coupling means can include at least one projectionwhich extends into the groove to hold the coupling means against axialmovement relative to the piston and/or vice versa. The first section ofthe coupling means can be provided with axially parallel slotsalternating with prongs or arms which bear upon and bias the sphericalhead against the one end of the piston. The first section of thecoupling means can be provided with an annular end portion whichsurrounds the aforementioned central opening and has a convex internalsurface which is maintained in substantially linear contact with thehead of the piston rod.

In accordance with another embodiment of the invention wherein the oneend of the piston surrounds at least a major portion of but normally theentire head of the piston rod, the coupling means can include asubstantially cup-shaped second section which comprises a tubularportion surrounding the one end of the piston and an annular end wallwhich surrounds the piston rod at the head. The one end of the pistonhas an external groove and the tubular portion of the second section hasat least one projection extending into the groove. The first section ofthe coupling means is confined in the second section and includes asleeve which reacts against the end wall of the second section and bearsupon the head of the piston rod.

In accordance with still another embodiment of the invention, thecoupling means can include or constitute a clip made of metallic wire orthe like. For example, the first section of a clip which constitutes thecoupling means can include prongs which abut the end face at the one endof the piston and engage the head of the piston rod, and the secondsection of such clip can include links which connect the prongs and arereceived in an internal groove of the one end of the piston. The firstsection of such clip can include two prongs and the second section caninclude two links which are received in the aforementioned groove bysnap action to urge the two prongs against the end face of the one endof the piston and against the head of the piston rod.

Alternatively, a clip which constitutes or forms part of the couplingmeans can comprise two legs which flank the piston rod and bear upon thehead to bias the head into a complementary socket in the one end of thepiston. The second section of the coupling means embodying orconstituting the clip is anchored in the one end of the piston by snapaction. The one end of the piston can be provided with radiallyextending slots for the second section of the clip. The latter can beU-shaped and its legs can be provided with arcuate median portions whichengage the head of the piston rod. The second section of such clip caninclude the first and second ends of the aforementioned legs and a webwhich connects the first ends of the legs to each other. The second endsof the legs can be provided with extensions in the form of teeth or thelike which are received in complementary recesses machined or otherwiseprovided in the one end of the piston.

In accordance with a further embodiment of the present invention, theone end of the piston is provided with a channel (e.g., with an axialbore or hole) which receives the head of the piston rod. The couplingmeans is at least partially confined in the channel and includes asleeve which surrounds the piston rod adjacent to the head of thelatter; the sleeve has a radially outwardly extending first end portionwhich constitutes the second section of the coupling means and isrecessed into the piston. An inwardly extending second end portion ofthe sleeve bears against the head of the piston rod and acts as thefirst section of the coupling means.

It is also possible to design the master cylinder in such a way that thehead of the piston rod is at least partially but preferably fullyconfined in the one end of the piston and that the second section of thecoupling means abuts the end face at the one end of the piston. Thefirst section of such coupling means is or can be provided with prongswhich are of one piece with the second section, which are anchored inthe one end of the piston and which abut the head of the piston rod. Theprongs can further serve as a means for centering the first section ofthe coupling means in the axial channel of the piston.

The first section of a further embodiment of the coupling means can beconfined in the second section and can include a sleeve which reactsagainst the second section and bears upon the head of the piston rod tobias the head into an internal socket provided in the one end of thepiston. At least a portion of such coupling means can consist of aplastic material and its first section can be provided with a concavesurface which abuts and is complementary to a convex external surface ofthe head.

The first section of a modified coupling means can be of one piece withthe second section; the first section of such coupling means abuts anend face at the one end of the piston and has a concave seat whichsurrounds the head of the piston rod. The second section of the couplingmeans has prongs which are externally adjacent the one end of the pistonand have projections extending into complementary recesses of the oneend of the piston.

In accordance with a further embodiment, the coupling means can comprisean elongated body which can resemble a bar confined in the one end ofthe piston. The second section of the coupling means constitutes a firstpart of the bar and is anchored in the piston, and the first section ofthe coupling means constitutes a second part of the bar and is anchoredin the head of the piston rod. The one end of the piston is providedwith internal tongs which engage the second section of the bar by snapaction.

The one end of the piston can have a diameter smaller than that of anadjacent median portion of the piston. A portion of the coupling meansis or can be mounted and configurated in such a way that its surroundsthe one end of the piston; such portion of the coupling means caninclude or constitute the second section.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved master cylinder itself, however, both as to its constructionand the mode of assembling its parts, together with numerous ad-titionalimportant and advantageous features and attributes thereof, will be bestunderstood upon perusal of the following detailed description of certainpresently preferred specific embodiments with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary axial sectional view of a master cylinderwherein the spherical head of the piston rod is articulately connectedwith the adjacent end of the piston by coupling means embodying one formof the present invention and constituting a wire clip;

FIG. 1a is an enlarged view of a detail including the structure withinthe phantom-line circle Z shown in FIG. 1;

FIG. 2 is a fragmentary axial sectional view of a piston, a fragmentaryelevational view of a piston rod and an axial sectional view of acoupling means made of sheet metal and configurated and mounted inaccordance with a second embodiment of the invention;

FIG. 3 is a view similar to that of FIG. 2 but showing a modifiedcoupling means having a section which is in mere linear contact with thespherical head of the piston rod;

FIG. 4 is a fragmentary axial sectional view of a piston, a fragmentaryelevational view of a piston rod having a spherical head which isconfined in the adjacent end of the piston, and a fragmentary axialsectional view of coupling means which is also confined in the piston;

FIG. 5 is a view similar to that of FIG. 4 but showing modified couplingmeans which urges the spherical head of the piston rod into acomplementary socket in the adjacent end of the piston;

FIG. 6 is a view similar to that of FIG. 5 but showing modified couplingmeans serving to hold the head of the piston rod in requisite engagementwith the internal socket of the piston;

FIG. 7 is a view similar to that of FIG. 5 or 6 but showing one-piececoupling means replacing the composite coupling means of FIGS. 5 and 6;

FIG. 8 is a view similar to that of FIG. 5, 6 or 7 but showing couplingmeans in the form of a clip which is designed to maintain the head ofthe piston rod in engagement with the internal socket of the piston;

FIG. 9 is an enlarged transverse sectional view as seen in the directionof arrows from the line IX—IX in FIG. 8;

FIG. 10 is a view similar to that of FIG. 8 but showing coupling meansin the form of a clip different from that shown in FIGS. 8 and 9;

FIG. 11 is a fragmentary front elevational view (as seen from theleft-hand side of FIG. 12) of a coupling means wherein the secondsection is of one piece with the first section and which is made of aplastic material;

FIG. 12 is a fragmentary axial sectional view of a piston, a fragmentaryelevational view of a piston rod, and an axial sectional view of thecoupling means of FIG. 11 in a position it assumes while articulatelyconnecting the head of the piston rod to the adjacent end of the piston;

FIG. 13 is a fragmentary axial sectional view of a piston, a fragmentarypartly elevational and partly sectional view of a piston rod, and alongitudinal sectional view of a coupling means which resembles anelongated bar and the sections of which are anchored in a centrallylocated core of the piston and in the head of the piston rod;

FIG. 14 is a fragmentary axial sectional view of a piston which is madeof a plastic material and corresponds to the piston shown in FIG. 6, afragmentary elevational view of a piston rod, and a fragmentary axialsectional view of coupling means corresponding to that shown in FIG. 6;and

FIG. 15 is a transverse sectional view of a piston rod and a similarsectional view of a piston constituting a modification of the pistonshown in FIG. 14.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a portion of a master cylinder 1 wherein two discretesections or cups 2, 6 of a composite housing define a plenum chamber 3for a reciprocable piston 8. The housing sections 2, 6 and the piston 8are made of a plastic material, and the section 2 is provided with anipple 5 constituting a fluid inlet and receiving (when necessary) ahydraulic fluid by gravity flow from a source, not shown, wherein thesupply of fluid is maintained at or close to atmospheric pressure. Anoutlet 4 can deliver pressurized fluid to a user (not shown), such asthe brake system or a clutch in the power train of a motor vehicle. Theinlet 5 can admit hydraulic fluid from the source into the chamber 3when the pressure in the chamber drops below the pressure in the source.

The right-hand part of the housing section 2 is enlarged and constitutesa cylindrical receptacle for the left-hand part of the housing section 6which latter surrounds the piston 8. The sections 2, 6 of the housingare or can be permanently secured to each other, e.g., by resorting to asuitable adhesive or to an ultrasonic welding technique. The piston 8 issnugly but reciprocably received in the cylindrical axial passage 7 ofthe housing section 6 and can draw or permit the fluid to flow from thesource, through the inlet 5, or expel pressurized fluid by way of theoutlet 4.

The plenum chamber 3 is sealed from the passage 7 by two axiallyspaced-apart annular sealing elements 9 a, 9 b which flank the inlet 5.

One end portion of a push rod or piston rod 10 has a spherical head 11extending into a complementary socket 12 in the adjacent end of thepiston 8. The parts 11, 12 constitute a swivel joint 13. The right-handend of the passage 7 in the housing section 6 is open and receives, withrequisite clearance, that part of the piston rod 10 which is adjacentthe head 11.

The coupling means 14 a which articulately connects the head 11 of thepiston rod 10 with the adjacent end of the piston 8 is constructed andinstalled and can operate in accordance with a first embodiment of thepresent invention. This coupling means 14 a is constituted by a clip 16which is made of metallic wire 17 and permits the head 11 to swivel inthe complementary socket 12 of the piston 8. The material of the clip 16is resilient so that the clip can engage the end portion of the pistonrod 10 and/or the piston 8 by snap action.

Certain details of the clip 16 and of the manner in which this clipcouples the head 11 to the adjacent end of the piston 8 are shown inFIG. 1a. The prongs 61 a, 61 b of the clip 16 have arcuate portionswhich flank the piston rod 10 immediately behind or at the head 11 andpreferably have arcuate median portions similar to those of the legs 43a, 43 b shown in FIG. 9. Such arcuate median portions follow theoutlines of the adjacent part of the piston rod 10 or its head 11; inaddition, the prongs 61 a, 61 b abut the adjacent end face of the piston8. The coupling means 14 a (and more specifically the clip 16) comprisesa first section which is constituted by the prongs 61 a, 61 b and servesto urge the head 11 against the socket 12 of the joint 13, and a secondsection which preferably releasably anchors the clip 16 in the adjacentend of the piston 8. The second section comprises links 60 a, 60 b whichextend from the prongs 61 a, 61 b into a groove 19 in the peripheralsurface 15 of the piston 8. The links 60 a, 60 b are connected to eachother by portions or webs 18 of the clip 16. The portions 18 areanchored in the groove 19 adjacent a collar 20 provided on the pistonrod 10 behind the head 11. The collar 20 serves as an abutment for theprongs 61 a, 61 b. The links 60 a, 60 b constitute the end portions ofthe respective prongs 61 a, 61 b.

The prongs 61 a, 61 b are or can be in mere linear contact with the head11; this is desirable and advantageous in many instances because itentails a reduction of wear upon the clip 16 as well as upon the head11. The connection between the head 11 and the first section (prongs 61a, 61 b) of the clip 16 (i.e., of the coupling means 14 a) is aso-called form-locking connection, and the second section 60 a, 18, 60 bof the clip 16 engages the end of the piston 8 (in the recess 19) bysnap action. Such second section also engages the extension 20 of thepiston rod 10.

The piston 8 can be made of a thermoplastic or a thermosetting plasticmaterial, preferably a phenolic resin reinforced by suitable filler orfillers so that its strength matches or approximates that of aluminum.Another advantage of such plastic material is its pronounced resistanceto wear as well as its ability to prevent undesirable (untimely)separation of the piston rod 10 from the piston 8. All this contributesto stability and reliability of the master cylinder 1.

The illustrated socket 12 can be replaced with a much larger socket, forexample, with a socket which receives one-half of the spherical head 11.

The introduction of a portion of the head 11 into the socket 12 of thethus obtained joint 13 can immediately precede the mounting of the clip16 in such a way that the first section 61 a, 61 b of the clipform-lockingly engages the piston rod 10 to bias the head 11 against theconcave surface in the socket 12 as soon as the second section 60 a, 18,60 b of the clip 16 engages the end of the piston 8 by snap action. Theforce which is being applied to the head 11 by the prongs 61 a, 61 bacts in the direction of the common axis of the piston 8 and housingsection 6 and suffices to maintain the joint 13 in the assembledcondition shown in FIG. 1, namely in a condition in which the sphericalexternal surface of the head 11 bears upon the complementary concavesurface in the socket 12 without any or without any appreciable play.

The piston 8 can be mass-produced in a suitable machine, e.g., in aninjection molding machine. Such mode of making the piston exhibits theadvantage that the piston is ready for use without any secondarytreatment, and this contributes to lower cost of the piston and of theentire master cylinder 1. Even the surface bounding the recess or groove19 and/or the end face which abuts the prongs 61 a, 61 b need notundergo any secondary treatment if the piston 8 is made in an injectionmolding machine.

The master cylinder 1, and particularly its piston 8 and the couplingmeans 14 a (including the clip 16) can be modified in a number of wayswithout departing from the spirit of the invention. For example, theclip 16 can be installed in such a way that its first section cannotcome into direct contact with the head 11 and/or with other parts of thepiston rod 10. This can be achieved by resorting to a ring-shaped ortubular washer which is installed between the end face of the piston 8and the prongs 61 a, 61 b and/or between such prongs and the head 11 tothus prolong the useful lives of the parts 8 and 14 a. Additionalinserts can be provided between the piston 8 and the second section 60a, 18, 60 b of the clip 16. The wire 17 of the clip 16 can be made of orcoated with a highly wear-resistant material; for example, the clip 16can be made of spring steel. The configuration(s) of that additionalpart or those additional parts which is or are interposed between thehead 11 and the coupling means 14 a is or are preferably such that eachpart contacting the head has a surface complementary to the sphericalsurface of the head. As a rule, each additonal part is or can be made ofa suitable plastic material which may but need not be the same as thatof the piston. All that counts is to select the material(s) and theconfiguration(s) of the additional part(s) in such a way that the wearupon the piston 8 and upon he piston rod 10 (including the head 11) isreduced as much as possible in order to prolong the useful life of themaster cylinder. If an additional part is a ring which transmits forcefrom the first section of the selected coupling means to the head of thepiston rod and thence to the socket of the piston, the ring can be madeof an elastomeric material and can be installed in stressed condition tourge the head 11 against the socket 12 without play. This can beachieved, for example, by employing a relatively thick ring which iscompressed when the coupling means connects the piston rod with thepiston.

The piston 8 of FIG. 2 is similar to the similarly referenced piston ofFIGS. 1 and 1a. The piston rod 10 of FIG. 2 is different from the pistonrod of the master cylinder 1 shown in FIGS. 1 and 1a because it need notbe provided with a collar 20. The coupling means 14 b of FIG. 2 is madeof a metallic sheet material and includes a hollow spherical firstsection 23 which surrounds a portion of the head 11 in a regionimmediately adjacent the non-spherical part of the piston rod 10, and atubular second section 21 which surrounds the adjacent end of the piston8 and has one or more projections (e.g., in the form of one or morebeads or a circumferentially complete internal rib) received by snapaction in the complementary recess or recesses 22 in the peripheralsurface of the piston.

The piston 8 includes an end portion having a first outer diameter andbeing surrounded by the tubular second section 21 of the coupling means14 b, and a median portion having an outer diameter exceeding that ofthe end portion and being slidably received in the housing section 6(not shown in FIG. 2) of the master cylinder including the structure ofFIG. 2. In this respect, the configurations of the pistons 8 shown inFIGS. 1, 1 a, 3, 5, 6, 12 and 14 are similar to that of the justdescribed piston of FIG. 2.

The configuration of the internal surface of the first section 23 iscomplementary to that of the adjacent portion of the head 11.

A difference between the structures shown in FIGS. 2 and 3 is that thefirst section 23 of the coupling means 14 b has a concave surfaceconfronting and contacting the adjacent portion of the external surfaceof the head 11, whereas the coupling means 14 c of FIG. 3 comprises afirst section 26 having a concave internal surface 25 in mere or insubstantially linear contact with the spherical surface of the head 11shown in FIG. 3. The second section 24 of the coupling means 14 c istubular and comprises a radially inwardly bent end portion which isreceived in the circumferential groove 22 provided in the end of thepiston 8. The tubular second section 24 of the coupling means 14 c doesnot extend radially outwardly beyond the larger-diameter median or mainpart of the piston 8 shown in FIG. 3.

The first section 26 of the coupling means 14 c has a central opening 25which spacedly surrounds the adjacent portion of the head 8. The section26 is provided with at least one but preferably two or more axiallyparallel slots (not shown in FIG. 3) which alternate with prongs ortongues bearing against the adjacent portions of the external surface ofthe head 11 to thus couple the piston rod 10 to the piston 8 by snapaction. Analogous axially parallel alternating slots and tongues orprongs are provided in the first section 23 of the coupling means 14 bshown in FIG. 2.

The coupling means 14 b and/or 14 c can be produced of sheet metal in adeep drawing machine. This contributes to a reasonable cost of suchcoupling means. An advantage of the first section 26 over the firstsection 23 is that the section 26 can be more readily slipped onto thehead 11. On the other hand, the first section 23 is in larger(surface-to-surface rather than substantially linear) contact with thehead 11.

The master cylinder embodying the structure of FIG. 4 departs from thoseembodying the structures shown in FIGS. 1, 1 a, 2 and 3 in that theentire coupling means 14 d is confined in the axial channel or passage32 of the piston 8. The first section 29 of the coupling means 14 d(which can be made of a metallic sheet material) has a concave surfacewhich bears upon the adjacent portion of the spherical surface on thehead 11 adjacent the non-spherical part of the piston rod 11. Thesleeve-like second section 28 of the coupling means 14 d is snuglyreceived in the axial channel 32 and has one or more radially outwardlyextending portions received by snap action in an internal groove 27provided in the respective end of the piston 8 shown in FIG. 4. Thecoupling means 14 d can be said to constitute a sleeve or tube one endportion of which constitutes the first section (serving to bias the head11 against the internal socket of the piston 8, and the other endportion of which comprises or constitutes the second section which isanchored in he end of the piston (i.e., in the internal groove 27) bysnap action. The arrangement can but need not be such that each radiallyoutwardly extending portion of the second section 28 fills thecorresponding part of the internal groove 27, i.e., that the connectionbetween the second section 28 and the piston 8 is a form-lockingconnection.

The head 11 of the piston rod 10 shown in FIG. 5 is caused to bearagainst a concave internal surface in the channel 32 of the piston 8under the action of a first section 30 forming part of the couplingmeans 14e and having a concave annular surface 33 bearing against theexternal surface of the head 11 adjacent the nonspherical part of thepiston rod 10. That end portion (31) of the first section 30 which isremote from the concave surface 33 constitutes a composite ring whichreacts against the adjacent internal surface of a radially extendingannular end wall 36 forming part of a cup-shaped second section 35having one or more radially inwardly extending projections 34 receivedby snap action in the external groove 22 machined into or otherwiseprovided in the external surface 22 of the end of the piston 8.

The aforementioned ring-shaped portion 31 of the first section 30 isconfined between the end wall 36 and the end face of the piston 8. Thesection 30 is slotted and, when its portion 31 is properly receivedbetween the end wall 36 and the end face of the piston 8, the section 30is centered in the channel 32 and the surface 33 maintains the head 11in optimal contact with the concave surface forming part of the socketin the piston 8. The slot in the section 30 is preferably a meanderingslot. The first section 30 is made of a plastic material and the secondsection 35 is or can be made of a metallic sheet material.

The coupling means 14 f of FIG. 6 differs from the coupling means 14 ein that its first section 37 is a plastic sleeve which is fitted intothe adjacent end of the channel in the piston 8, which reacts againstthe end wall 36 of the cupped second section 35, and which bears uponthe spherical head 11 of the piston rod 10 to thus urge the head againstthe internal socket of the piston 8.

The master cylinder including the piston 8 and the piston rod 10 of FIG.7 employs one-piece coupling means 14 g made of a plastic material andincluding a first section 41 fitted into the end portion of the channel32 and having a concave surface bearing upon the head 11. The secondsection 39 of the coupling means 14 g has a ring-shaped end abutting theend face of the piston 8 and axially parallel studs or prongs or tonguesreceived in complementary recesses 40 provided in the end of the piston.The prongs are or can be of one piece with the aforementionedring-shaped end of the second section 39.

It is often desirable to permanently secure the second section 39 to thepiston 8 of FIG. 7, e.g., by ultrasonic welding or by resorting to asuitable adhesive substance.

FIGS. 8 and 9 illustrate a piston 8, a piston rod 10 and coupling means14 h serving to separably retain the head 11 of the piston rod incontact with the internal socket of the piston. The coupling means 14 his analogous to the coupling means 14 a of FIGS. 1 and 1a because italso comprises a (U-shaped) clip which is held in radially extendingslots 42, 46 provided in the hollow end of the piston 8. The couplingmeans 14 h includes two elongated legs or prongs 43 a, 43 b havingarcuate median portions which directly engage the head 11 at itsconnection or junction with the adjacent part of the piston rod 10,i.e., the legs 43 a, 43 b constitute the first section of the couplingmeans 14 h. The second section of the coupling means 14 h comprises thefirst and second end portions of the legs 43 a, 43 b; the first endportions of these legs are integral with a connecting web which alsoforms part of the second section and is received in the radial recess 42of the piston 8. The second end portions of the legs 43 a, 43 b tend tomove apart and respectively have lateral extensions 44 a, 44 b receivedby snap action in recesses 45 a, 45 b communicating with the radiallyextending slot 46 in the respective end of the piston 8.

FIGS. 8 and 9 show that the clip-shaped coupling means 14 h extendsradially of the end of the piston 8. Such coupling means can be made ofmetallic wire and its second section (including the web and theextensions 44 a, 44 b can be assembled with the piston 8 into a modulewhich is ready to receive the head 11 of the piston rod 10.

If it is desired to avoid direct contact between the arcuate medianportions of the legs 43 a, 43 b and the head 11, the coupling means 14 hof FIGS. 8 and 9 can further comprise a sleeve-like insert made of aplastic or other suitable material; for example, the coupling means 14 hcan employ a sleeve-like insert (resembling the plastic sleeve 37 ofFIG. 6) which reacts against the arcuate portions of the legs 43 a, 43 band bears upon the head 11 of the piston rod 10.

The coupling means 14 i of FIG. 10 employs or is a clip which is made ofwire and includes legs 38 constituting the second section of suchcoupling means. The first section of the coupling means 14 i comprises asleeve 37 which reacts against the section 38 and has a concave annularsurface which is urged against the head 11 so that the latter remains incontact with the concave surface of the socket in the piston 8. Thedimensions of the coupling means 14 i are selected in such a way thatthe section 37 bears upon the head 11 with a force which holds the headagainst movement away from the socket or seat in the piston 8, i.e.,against movement axially and away from the closed left-hand end of thepiston.

The coupling means 14 j of FIGS. 11 and 12 is a onepiece plastic bodyhaving a first section 49 with a concave annular surface 51 bearing uponthe head 11 of the piston rod 10 so that the head is urged against thesocket in the end of the piston 8, and a second section includingaxially parallel prongs 47 recessed into the peripheral surface of theillustrated end of the piston 8 and having projections 48 received inthe external groove 22 of the piston by snap action. The first section49 can be said to constitute a slotted annular end wall which abuts theend face of the piston 8 and has a central opening 50 for the shank ofthe piston rod 10, i.e., for that part of the piston rod which isimmediately adjacent the head 11.

FIG. 11 shows that the first section 49 of the plastic coupling means 14j comprises six equidistant axially parallel prongs each having aprojection 48 engaging, by snap action, a portion of the surfacebounding the external groove 32 of the piston 8.

The first section 49 of the coupling means 14 j is slotted radially tothus permit a spreading apart of the first section preparatory tointroduction of the piston rod 10 into the central opening 50. The slotof the section 49 extends between two prongs of the second section 47.Neighboring projections 48 can be connected to each other.

In assembling the structure of FIGS. 11, 12 into a module, one willassemble the coupling means 14 j with the piston rod 10, and the thusobtained first module is thereupon assembled with the piston 8 to formtherewith a second module ready to be installed in the housing of amaster cylinder. In the assembled condition of the master cylinderembodying the structure of FIGS. 11 and 12, the first section 49 of thecoupling means 14 j abuts the end face of the piston 8; this ensuresthat the concave surface 51 abuts the head 11 and the head abuts theinternal socket of the piston 8. Assembly of the coupling means 14 jwith the piston rod 10 involves an opening up of the section 49, i.e., awidening of its radial slot so that the section 49 can be placed aroundthat part of the piston rod which is adjacent the head 11. The section49 thereupon closes due to its memory and the second section 47 is readyto have its prongs slipped along the external surface of thesmaller-diameter end of the piston 8 until the projections 48 snap intothe groove 22.

The structure of FIGS. 11 and 12 is particularly suitable for automaticassembly of master cylinders and for automatic installation of suchmaster cylinders in a motor vehicle, e.g., to engage the brakes or toengage a clutch.

FIG. 13 shows a portion of a master cylinder wherein the piston 8receives the head 11 of the piston rod 10 and wherein the coupling means14 k comprises an elongated flexible rod or bar having a first section54 anchored in the head 11 and a second section 52 anchored in the spacebetween the tongs 53 of the piston 8. The tongs 53 can constitute theprongs of a longitudinally slotted sleeve or core spacedly surrounded bythe cylindrical outer wall of the piston 8. The just discussed core canconstitute a separately produced part which is installed in the axialpassage or channel of the piston 8, or an integral part of the piston(see 55 in FIG. 14).

The first section 54 of the elongated rod- or bar-shaped coupling means14 k can be permanently anchored in the head 11 of the piston rod 10. Inorder to ensure that the piston rod 10 can swivel at least in directionsindicated by a double-headed arrow, a portion of the first section 54 isreceived in the head 11 with a certain amount of clearance whichsuffices to permit all necessary movements of the piston rod 10 and thepiston 8 relative to each other.

The structure of FIG. 13 can be employed with advantage in mastercylinders which are designed for automatic assembly of their parts.Furthermore, the piston 8 can be readily maintained in a position ofexact axial alignment with the piston rod 10; this is desirable forconvenient installation of the master cylinder in a motor vehicle.Permanent attachment of the coupling means 14 k to the head 11 of thepiston rod 10 is optional but often desirable.

FIG. 14 illustrates one presently preferred mode of making the piston 8from a suitable plastic material, preferably in an injection moldingmachine and in such a way that the piston can be properly engaged byseveral types of coupling means, for example, the coupling means shown(at 14 f ) in FIG. 6. The piston 8 of FIG. 14 is made of a thermosettingmaterial and comprises a centrally located portion or core 55 which canbe said to constitute a socket or seat having a concave surface 56serving as an abutment for the head 11. The funnel-shaped central recess57 is provided in order to facilitate or simplify the injection moldingoperation; this recess is adjacent the plenum chamber of the housingwhich receives the piston 8 of FIG. 14 in the assembled condition of themaster cylinder embodying the structure of FIG. 14.

FIG. 15 shows a piston 8 having internal ribs 58 with integral radiallyinnermost portions which define a ram-like member 59 having a diametersmaller than that of the centrally located core 55 shown in FIG. 14. Themember 59 and (if necessary) the ribs 58 have concave surfaces servingas abutments for the head 11 of the piston rod.

The exact configuration of the coupling means depends upon the preferredor desired mode of assembling a complete master cylinder. For example,the coupling means can be designed in such a way (see, e.g., FIG. 4)that the piston 8 and the piston rod 10 can be assembled into a modulebefore the piston is inserted into the housing of the master cylinder.On the other hand, different coupling means can be particularly suitedfor use as a means for installing the head of a piston rod in the socketof a piston which is already installed in the housing of a mastercylinder (see, for example, the coupling means 14 b of FIG. 2).

The extent to which a coupling means can be opened up or expandedpreparatory to attachment of the piston rod to the piston also dependson the sequence of assembling the parts of a master cylinder and/or uponthe selected type of coupling means. For example, the tubular secondsection 21 of the coupling means 14 b should be slotted in order topermit convenient application over the smaller-diameter end of thepiston 8 and the penetration of the projection(s) of such second sectioninto the groove 22 of the piston.

The cost can also constitute an important factor in selecting the natureof coupling means to be utilized in the improved master cylinder. Forexample, a coupling means (such as 14 h shown in FIGS. 8 and 9) whichconstitutes a single piece of suitably shaped wire can be mass-producedat a reasonable cost, and it can be assembled with the parts 8, 10 in atime-saving manner. A coupling means (such as 14 h ) can be simplifiedby replacing the legs 43 a, 43 b with straight legs which extendtangentially of the piston rod 10, i.e., which are in a mere pointcontact with the head 11 or with that part of a piston rod 10 which isadjacent the head. The provision of legs (43 a, 43 b ) with arcuateportions which are in linear (rather than mere point) contact with thepiston rod is preferred in many instances because this entails adistribution of pressures between the coupling means and the piston rodover a relatively large area of the head 11 and/or over the adjacentpart of the piston rod. In other words, the wear upon the piston rodand/or upon the coupling means can be reduced.

The utilization of coupling means (14 d ) of the type shown in FIG. 4exhibits the advantage that the master cylinder can employ a very simpleand inexpensive piston. Thus, the piston 8 of FIG. 4 must be providedonly with an internal socket for the head of the piston rod and with aninternal groove (27) for the second section (28) of the coupling means(14 d ), i.e., the external surface of the piston can constitute a plaincylinder without any grooves, smaller- and larger-diameter portions orthe like, and the end face of the piston need not undergo any finishingtreatment.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic and specific aspects of the aboveoutlined contribution to the art of master cylinders and, therefore,such adaptations should and are intended to be comprehended within themeaning and range of equivalence of the appended claims.

What is claimed is:
 1. A master cylinder, comprising: a housing defininga chamber; a piston reciprocable in said chamber and having first andsecond ends; a reciprocable piston rod including a spherical headextending into said chamber; and means for articulately coupling saidhead to one end of said piston, including a first section engaging saidhead and a second section affixed to said piston; wherein said firstsection of said coupling means is a portion of a hollow sphere whichsurrounds and bears upon a portion of said head and has a centralopening remote from said second section and surrounding a portion ofsaid piston rod; wherein said piston rod further includes an elongatedpart having an end connected with said head, said first sectionsurrounding said head at said end of said elongated part and said secondsection including a tubular portion surrounding said one end of saidpiston; wherein said one end of said piston has an external groove andsaid second section of said coupling means comprises at least oneprojection extending into said groove.
 2. The master cylinder of claim1, wherein said piston contains a plastic material and at least aportion of said coupling means consists of a metallic sheet material. 3.The master cylinder of claim 2, wherein said first section of saidcoupling means is a portion of a hollow sphere which surrounds and bearsupon a portion of said head and has a central opening remote from saidsecond section and surrounding a portion of said piston rod.
 4. Themaster cylinder of claim 3, wherein said piston rod further includes anelongated part having an end connected with said head, said firstsection surrounding said head at said end of said elongated part andsaid second section including a tubular portion surrounding said one endof said piston.
 5. The master cylinder of claim 4, wherein said firstsection of said coupling means has slots alternating with prongs whichbear upon and bias said head against said one end of said piston.
 6. Themaster cylinder of claim 4, wherein said first section of said couplingmeans has an annular end portion surrounding said central opening andhaving a concave internal surface in substantially spherical contactwith said head.
 7. A master cylinder, comprising: a housing defining achamber; a piston reciprocable in said chamber and having first andsecond ends; a reciprocable piston rod including a spherical headextending into said chamber; and a means for articulately coupling saidhead to one end of said piston, including a first section engaging saidhead and a second section affixed to said piston; wherein said one endof said piston surrounds at least a major portion of said head, saidsecond section of said coupling means being cup-shaped and including atubular portion surrounding said one end of said piston and an annularend wall surrounding said piston rod at said head, said one end of saidpiston having an external groove and said tubular portion of said secondsection having a projection extending into said groove, said firstsection being confined in said second section and including a sleevereacting against said end wall and bearing upon said head.
 8. A mastercylinder, comprising: a housing defining a chamber; a pistonreciprocable in said chamber and having first and second ends; areciprocable piston rod including a spherical head extending into saidchamber; and a means for articulately coupling said head to one end ofsaid piston, including a first section engaging said head and a secondsection affixed to said piston; wherein said one end of said piston hasa first outer diameter and said piston further comprises a medianportion having a second outer diameter exceeding said first diameter, aportion of said coupling means surrounding said one end of said piston.9. The master cylinder of claim 8, wherein said portion of said couplingmeans forms part of said second section.